The objective of this program is to study the infectious agents resident in human dental plaque which are involved in the etiology of dental caries and peridontal disease, and to seek ways of preventing these infections. The program encompasses a spectrum of studies ranging from those aimed at providing fundamental knowledge of the ecology of odontopathic bacteria to those where the effectiveness of chemotherapeutic agents are being assessed for practical control of dental infections. The types of bacteria present in human carious lesions and those associated with the extremes of peridontal health and disease will be investigated. The odontopathic potential of prominent groups of organisms will be assessed singly and in combination with already recognized odontopathic bacteria in experimental animals. Techniques to facilitate the identification and enumeration of recognized odontopathic bacteria will be developed. Special attention is being devoted to the Gram-positive filamentous rods which are numerically prominent in human dental plaque and which include members with recognized pathogenic potential. Ecological determinants responsible for the establishment of odontopathic bacteria in the oral cavity will be investigated placing particular emphasis upon the nature of their surface components and the mechanisms they use for adhering to teeth and other oral surfaces. Parameters affecting the growth and mode of transmission of these organisms from individual to individual as well as their spread within the human oral cavity will be investigated. The possible chemotherapeutic value of antibiotics and disinfectants for the control of Streptococcus mutans populations on teeth in humans will be studied. Collectively the information obtained will be used to attempt to devise practical means of either preventing initial infection by odontopathic bacteria or ways of controlling such organisms once infection has incurred.